This invention relates in general to earth boring bits, and in particular to a solid head bit with a wear resistant core containing a nozzle passage and at least one cutting element.
Most oil and gas wells are drilled with rolling cutter bits. In some formations, however, solid head bits have been found to be more efficient. These solid head bits are of steel and have a lower face within which a number of cutting elements are secured in holes. Each cutting element has a cylindrical tungsten carbide stud located in the hole, and a flat cutting edge bonded to the stud and facing in the direction of rotation. The cutting edge consists of polycrystalline diamond on a tungsten carbide substrate.
Each drill bit has an axial drilling fluid passage with one or more outlets. To reduce erosion of the steel body of the bit, a tungsten carbide nozzle is located at the outlet. For good bottom hole coverage, it is desirable to place some of the cutting elements close to the nozzles. However, because of the hole required for the stud, and the necessary supporting metal around each stud hole, it is difficult to place the cutting elements in the optimum positions. Erosion of the supporting metal occurs if the cutting element is placed too close to the nozzle, resulting in a loss of the element.
In U.S. Pat. No. 4,303,136, Harry N. Ball, Dec. 1, 1981, a cutting element with a flat cutting edge is shown with a passage formed through the base of the cutting element. The purpose of the passage is to discharge drilling fluid across the cutting edge. However, the passage appears likely to be subject to plugging because of its small diameter.